Mechanics and tribology of micro- and nanolayered PVD coatings

Abstract: Thin coatings produced by physical vapour deposition (PVD) are increasingly applied tomechanical components such as metal cutting tools, forming tools and machine elements.Improved micro- and nanolayered PVD coatings have been studied with respect tomechanical and tribological properties.The importance of residual stresses on crack initiation and delamination of coatings has been revealed. Numerical calculations supported by experimental studies have been used to predict and visualise these often detrimental stresses.A procedure which permits the elastic modulus and residual stress of the coating to be determined simultaneously was proposed, avoiding the limitation of small deflections in Stoney's equation and allowing improved accuracy. A four-point bending device aimed for investigations of micro scale coating fracture phenomena in-situ in an SEM was constructed and used to quantify cracking resistances of TiN and CrN coatings. Bending of coatings with different materials and lamella thicknesses proved the toughening of coatings achieved through multilayering. Both nitride and carbide multilayer coatings were tested in sliding contact. Especially, surface chemistry and oxidation were shown to be more important for friction and wear in this test than the coating hardness. TiN/MoN and Tic/C were found to be very promising coatings.A new and more detailed description of the abrasive wear of multilayer coatings is presented, based on experiments with Cr/CrN coatings with different lamella thicknesses. A new hydrocarbon free PVD process was developed and used to deposit TiC/C coatings. The process allows for tailoring of material properties such as coating hardness, residual stress and modulus of elasticity. These coatings also provided very low frictioncoefficients, 0.15 against steel.